The generic function
stream-read-sequence reads from stream into sequence. Elements from the start of sequence are replaced by elements from stream until end in sequence or the end-of-file in stream is reached. The index of the first element in sequence that is not replaced is returned.
A default method is provided by
fundamental-character-input-stream which makes repeated calls to
stream-read-char and uses
(setf elt) to insert characters into sequence. A default method is provided by
fundamental-binary-input-stream that makes repeated calls to
stream-read-byte and also uses
(setf elt) to insert bytes into sequence. Note that this may lead to error if the sequence is of inappropriate type.
LispWorks User Guide and Reference Manual - 20 Sep 2017